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[Labi1995]

The results of the ACE study also match my very rough estimate of the percentage of the Vibram Fivefingers runners who were heel striking at the NYC Barefoot Run last Sunday (see video below for example – I have not tallied any numbers, just a rough guess from watching the video – barefooters seemed to be much more likely to forefoot strike).If the data presented here are correct, and that any form of heel strike when barefoot or in a minimal shoe like the Vibrams will dramatically increase loading rate, then individuals who continue to heel strike when barefoot or in the Vibrams may be at risk (if in fact loading rate increases injury risk). Personally, I’d like to see data on if/how vertical loading rate varies with foot contact angle, knee flexion, and distance of contact from the center of mass among the heel striking runners. Is it possible to run barefoot or in Vibrams safely with a heel strike? Maybe, perhaps if an individual is strong and other aspects of their mechanics are good (see this post by Jay Dicharry for more on this). It’s also worth noting that even if loading rate is a risk factor for injury, that does not mean that if you have a high loading rate, you are guaranteed to get hurt. It’s merely an association, and some individuals may be able to tolerate a high loading rate better than others.Perhaps what I find most interesting from the ACE study, as well as the film I have from the NYC Barefoot Run, is that it suggests that old habits can be hard to break. Your body learns how to run at a very young age, and most of us have done so with shoes on our feet (probably stiff or heavily cushioned shoes). When you look at Daniel Lieberman’s data for Kenyan kids who have never before worn shoes, they either midfoot or forefoot strike 90% of the time when barefoot. What would happen if > they put on a pair of Vibrams? I don’t know, but it would be fascinating to find out. I’m doubtful that they would start heel striking.My personal hypothesis is that we develop the specifics of our running form early in life, and what that running form looks like is influenced by our childhood footwear. I’m watching my 18 month old son learn to run right now, and some of his playmates are already in big, bulky running shoes. Once we start our childhood path in athletic shoes, it rarely deviates from the heel-lifted, heavily cushioned variety. As adults, we get to a point where some of us decide to take off our cushioned trainers (perhaps out of a desire to shed an injury, or simply due to curiosity) and try out a pair of minimal shoes like Vibrams. We expect miracles to happen, and, indeed, some of us switch our foot strike immediately and old injuries seem to disappear, probably due to altering individually problematic patterns of force application to our feet and legs. However, others (as many as 50% if the numbers are correct!), for whatever reason, do not. Why? That, to me, is the big question.I think there is probably a big motor learning component here, and though some form adaptations (e.g., joint angles) may occur instantaneously, wholesale changes to highly ingrained movement patterns may just be hard for some people to accomplish. I’m not a psychologist, and my attempt to discuss motor learning variability with a colleague in the Psych Dept. upstairs from me led me to realize I have a lot of reading to do. The disparity in response among individuals to altering footwear condition fascinates me. For those who don’t switch right away, could form change be facilitated via cueing and coaching? Perhaps, and studies of real-time gait retraining have been shown the technique to be effective.Can some individuals accomplish form change with additional practice? Well, I can address that to an extent – here’s a video of me from two years ago, this was the first time I ever ran barefoot as an adult:Clearly, I was heel striking in the video, and it took enormous effort to retrain my gait. Quite honestly, I’m sure I still do more than my fair share of heel striking when I run, particularly in more built up shoes, but at least a midfoot/forefoot stride no longer feels awkward when I am doing it (and I’m pretty certain that I don’t heel strike when I run barefoot). Practice is surely important, but it’s hard to say just how much practice it might take for any given individual to achieve form change.